Bottom Line:
The models were then used to evaluate the protective effect of soluble collagen in the UVA crosslinking system.Enzyme treatments resulted in corneal curvature changes, collagen ultrastructural damage, decreased swelling resistance and thermal stability, which are similar to what is observed in keratoconus eyes.UVA crosslinking restored swelling resistance and thermal stability, but ultrastructural damage were found in the crosslinked ectatic corneas.

Affiliation: Wilmer Eye Institute, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America.

ABSTRACTCollagen crosslinking is a relatively new treatment for structural disorders of corneal ectasia, such as keratoconus. However, there is a lack of animal models of keratoconus, which has been an obstacle for carefully analyzing the mechanisms of crosslinking and evaluating new therapies. In this study, we treated rabbit eyes with collagenase and chondroitinase enzymes to generate ex vivo corneal ectatic models that simulate the structural disorder of keratoconus. The models were then used to evaluate the protective effect of soluble collagen in the UVA crosslinking system. After enzyme treatment, the eyes were exposed to riboflavin/UVA crosslinking with and without soluble type I collagen. Corneal morphology, collagen ultrastructure, and thermal stability were evaluated before and after crosslinking. Enzyme treatments resulted in corneal curvature changes, collagen ultrastructural damage, decreased swelling resistance and thermal stability, which are similar to what is observed in keratoconus eyes. UVA crosslinking restored swelling resistance and thermal stability, but ultrastructural damage were found in the crosslinked ectatic corneas. Adding soluble collagen during crosslinking provided ultrastructural protection and further enhanced the swelling resistance. Therefore, UVA crosslinking on the ectatic model mimicked typical clinical treatment for keratoconus, suggesting that this model replicates aspects of human keratoconus and could be used for investigating experimental therapies and treatments prior to translation.

pone.0136999.g005: Differential scanning calorimetry thermograms of ectatic corneas before and after crosslinking.

Mentions:
The DSC thermograms highlighted the matrix thermal stability changes after enzyme treatments (Fig 5). All samples presented one peak, which related to the temperature of thermal denaturation of collagen. After degradation, the transit temperature of COLG group and the ChaseABC group shifted to the lower temperature range (Table 3). After UVA crosslinking (with or without soluble collagen), the transition temperature increased as compared to the corneas with the same treatment.

pone.0136999.g005: Differential scanning calorimetry thermograms of ectatic corneas before and after crosslinking.

Mentions:
The DSC thermograms highlighted the matrix thermal stability changes after enzyme treatments (Fig 5). All samples presented one peak, which related to the temperature of thermal denaturation of collagen. After degradation, the transit temperature of COLG group and the ChaseABC group shifted to the lower temperature range (Table 3). After UVA crosslinking (with or without soluble collagen), the transition temperature increased as compared to the corneas with the same treatment.

Bottom Line:
The models were then used to evaluate the protective effect of soluble collagen in the UVA crosslinking system.Enzyme treatments resulted in corneal curvature changes, collagen ultrastructural damage, decreased swelling resistance and thermal stability, which are similar to what is observed in keratoconus eyes.UVA crosslinking restored swelling resistance and thermal stability, but ultrastructural damage were found in the crosslinked ectatic corneas.

Affiliation:
Wilmer Eye Institute, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America.

ABSTRACTCollagen crosslinking is a relatively new treatment for structural disorders of corneal ectasia, such as keratoconus. However, there is a lack of animal models of keratoconus, which has been an obstacle for carefully analyzing the mechanisms of crosslinking and evaluating new therapies. In this study, we treated rabbit eyes with collagenase and chondroitinase enzymes to generate ex vivo corneal ectatic models that simulate the structural disorder of keratoconus. The models were then used to evaluate the protective effect of soluble collagen in the UVA crosslinking system. After enzyme treatment, the eyes were exposed to riboflavin/UVA crosslinking with and without soluble type I collagen. Corneal morphology, collagen ultrastructure, and thermal stability were evaluated before and after crosslinking. Enzyme treatments resulted in corneal curvature changes, collagen ultrastructural damage, decreased swelling resistance and thermal stability, which are similar to what is observed in keratoconus eyes. UVA crosslinking restored swelling resistance and thermal stability, but ultrastructural damage were found in the crosslinked ectatic corneas. Adding soluble collagen during crosslinking provided ultrastructural protection and further enhanced the swelling resistance. Therefore, UVA crosslinking on the ectatic model mimicked typical clinical treatment for keratoconus, suggesting that this model replicates aspects of human keratoconus and could be used for investigating experimental therapies and treatments prior to translation.